This invention relates to gas turbine machines and relates more particularly to axial flow type gas turbine machinery having a rotating turbine wheel.
Turbomachines of the type described normally include a turbine wheel that is rotatably mounted to the machine housing through an axial thrust bearing. Blades on the wheel traverse a fluid flow duct and are arranged either to be rotated by flow in the duct or to induce and compress airflow through the duct. The turbine conventionally is made of high quality and high strength material (such as a titanium alloy) to withstand the stresses of rotational speeds of several thousand r.p.m., while the housing is of a light-weight material such as aluminum. Failure of the thrust bearing may create a hazardous condition since high energy fragments thrown from the titanium wheel may pierce the relatively thin housing and be expelled from the machine at a sufficiently high energy level to cause damage to surrounding components and structure. Additional damage can occur during failure as the result of the high temperature developed by the frictional contact between the wheel and hard materials carried by the housing. Such generated heat is normally entrained in and carried from the housing in the gas exhaust from the duct, thereby possibly creating an extremely high temperature exhaust airflow.
To reduce ejection of high energy wheel fragments, a containment ring may be incorporated in surrounding relationship to the wheel, such as described in U.S. Pat. No. 3,241,813. The containment ring is sufficiently strong and massive to prevent fragment penetration. For various purposes, including weight and space economy, the containment ring is of limited axial extent. Accordingly, upon failure of the thrust bearing and consequent axial shifting of certain turbine wheel arrangements due to external loads imposed thereon and/or the mass flow in the duct, the wheel may move past the axial confines of the containment ring before fragments thereof are ejected by centrifugal force. Thus, such fragments may not be retained in the housing by the containment ring. Further, due to the general unpredictability of events during such a failure, many such wheel fragments may be expelled.
It is a broad object of the present invention to provide in a gas turbine machine wherein the turbine wheel is subject to axial shifting to locations outside the confines of a containment ring upon occurrence of certain failures of the machine, apparatus and method for containing fragments of the wheel thrown centrifugally therefrom upon failure.
Another important object of the invention is to provide apparatus for absorbing heat generated upon failure of a gas turbine machine.
A more particular object is to provide apparatus in accordance with the preceding object which includes a pad of high heat absorption, low melting point material which frictionally engages a rotating turbine wheel of the machine upon failure in order to reduce temperature generated in the machine, and more particularly to reduce the maximum temperature developed in the flow of working fluid exhausting from the machine upon failure.
Yet another object of the invention is to provide severing means in a gas turbine machine which engage and sever the peripheral blades of a turbine wheel upon axial shifting of the latter as a result of failure of a thrust bearing rotatably mounting the turbine wheel within the machine housing. The severing means are located and arranged to sever the peripheral blades while the latter are within the confines of a containment ring normally radially surrounding the turbine wheel.
More particularly, the severing means includes a plurality of circularly arranged cutter pins that engage the wheel to sever the blades, the pins being embedded in, but extending a short axial distance from, a pad of high heat absorption material that presents a relatively large area of frictional contact with the wheel upon failure.
These and other objects and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings, wherein: